1. Field of the Invention
The invention relates to a pop shield for microphones, comprising a housing in which an electroacoustic transducer is arranged and a cover of an open-pore foam which, together with the housing, at least substantially encloses the electroacoustic transducer. In this connection, the invention particularly, but not exclusively, relates to microphones having a pop shield as an integral part thereof, i.e., arranged within their housing or a cage cover.
2. Description of the Related Art
The human speech has a number of so-called pop noises such as the letters p, t, k but also b and d which are characterized in that, even when they are pronounced with normal volume, they produce a sharp or sudden pressure wave. When this sound wave impacts on the diaphragm of the microphone, it causes an extreme or violent membrane movement and thus an overloading of the amplifier connected to the microphone. When playing back such a recording, this is recognizable as an unpleasant pop or plop noise.
In order to avoid this effect, according to the prior art a cover or shield is provided, usually made of foamed plastic material (referred to in the following as foam), that surrounds the diaphragm of the microphone, and, furthermore, a metal cage positioned externally and closely hugging the foam is provided as a mechanical protection of the foam as well as of the diaphragm. In other designs, a ball-shaped (spherical) or cube-shaped configurations of foam is placed onto the microphones, in particular, in the case of microphones which are used for on-site reporting. Tests have shown that such covers, which are simply slip on and are also referred to as wind screens, have no great efficiency. In the case of real wind screen devices, which are comprised of sleeves of foam and a fur-like coating arranged externally thereon, this is however different; these devices are indeed able to prevent wind noises and pop or plop noises occurring similar to wind noises.
It is known from U.S. Pat. No. 4,600,077 to provide an envelope for such external wind screen devices that are independent of the microphone. Such envelope is configured to surround the entire microphone and forms a net-like housing which is coated with suitable materials, in the aforementioned case, laminated fabric, in several layers.
In the case of studio microphones, where highest recording fidelity is to be observed and where the entire surroundings must be configured such that the best possible recording and transmission quality is ensured, no covers are used for the microphone capsule or diaphragm in order to prevent any type of distortion of the recording; instead, between the speaker and the microphone a corresponding mesh-like barrier is provided which fulfills the same task but is much more effective and has fewer side effects. Wind noises are, of course, not present in the studio so that indeed only the prevention of the pop noises must be ensured.
All of the aforementioned measures for preventing the pop noises have different disadvantages. For example, the foam envelopes or covers are either not really effective or, the more effective they are, the more they change the directional characteristic of the microphone and thus dampen its output level. The shields which are used in the studio are entirely unsuitable for use outside the studio, and there is therefore a need to provide an improvement of the pop shield, wherein particularly the occurrence of pop noises for direct voice input into the microphone at very close range is to be prevented without considerably affecting the output level, directional characteristic and frequency course of the microphone.
In accordance with the present invention, this is achieved in that the pop shield, at least in the main voice input direction of the microphone, is divided into two envelopes which are spaced apart from one another.
For microphones which are mostly used for voice input in one direction (for example, for rod-shaped lapel microphones in the axial direction), it is in this connection sufficient to provide between the speaker and the diaphragm, when viewed in the axial direction, two protective layers with an air space positioned therebetween wherein for a microphone that is to receive voice input from all directions an inner protector and an outer protector are preferably provided.
The invention is based on the recognition that the conventional pop shield covers, even when the wall thickness is increased, provide no considerable improvement of the pop shield effect but, instead, the output level, directional characteristic, and frequency course are changed. In comparison to conventional pop shield covers, the wall thickness can be considerably reduced without reducing be obtained pop shield effect.
It was surprisingly found that upon arranging two such covers at a spacing from one another an extreme improvement of the pop shield effect occurs without considerably changing or dampening the output level of the microphone or its directional characteristics and frequency course. The invention enables a significant improvement of the object of the invention by using pop shields or covers which, with regard to their total thickness, are hardly changed but are separated into two layers which are spaced from one another, wherein the spacing between the layers of the pop shield can be viewed as the important feature of the invention.